This invention relates to a pressure activated device and a method for use downhole in oil wells and the like. The device and method can be used to set devices such as packers and hangers which must be mechanically engaged with tubing.
Most setting mechanisms previously used have relied on elastomeric seals to prevent leaks between the tubing and the annulus, but the elastomers degrade with time and this arrangement gives poor reliability in completion strings.
Setting devices have previously been used in which sealing between the tubing and the annulus does not rely on elastomeric seals. Such devices use an electronic module and an explosive charge held within an atmospheric chamber. The electronic module monitors pressure pulse signals applied to the drill or completion string and in response to the correct code ignites the explosive charge to generate a high pressure gas. The gas in turn is used to apply hydraulic pressure to the tool to be set.
This type of setting tool is very complicated and has a number of disadvantages. Atmospheric chambers in the tool are inherently unreliable, and typically dependent upon the elastomeric seals, and in the event of leakage into the chamber the tool becomes inoperable. The electronic module is subject to temperature limitations, especially at depth. Since the explosive charge is housed within the atmospheric chamber, no pressure differential will be generated at the setting piston until the hydrostatic pressure outside the setting tool has been overcome by the charge pressure, which limits the setting load available and puts a depth limit on the setting tool.